This invention relates to light sensors and more particularly to an integrated circuit light sensor having essentially only two terminals and exhibiting a high photo-conductivity sensitivity that is stable with temperature.
Photo-diodes with two terminals, have long been known to exhibit photo-conductivity. Silicon diodes are known to provide low photo conductive sensitivity but are quite stable with temperature. On the other hand, photo-sensors made of cadmium sulfide are know to have much higher sensitivities that are much more subject to change as a function of temperature.
The integration of silicon photo-diodes with an amplifier in a unitary silicon integrated circuit has helped to realize a high sensitivity light-to-current transducer that offers a stability with temperature comparable to that of a simple silicon photo-diode. Such an integrated circuit employing a current-mirror amplifier is described by R. Genesi in U.S. Pat. No. 4,085,411 issued Apr. 18, 1978 and is assigned to the same assignee as the present invention. The output of the amplifier is taken as the collector of the output transistor that is in turn connected through a load to a DC supply buss. The load is typically another portion of the same integrated circuit and/or an external integrating capacitor.
It is an object of this invention to provide a two terminal photo-sensor, of the photo-conductor type, having a greater but similarly stable sensitivity to that of a simple silicon photo-diode.
It is a further object of this invention to provide such a two terminal photo-sensor having a sensitivity adjustment means for providing sensors of precisely predetermined sensitivity.